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Issue 36, 2012
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Azo-hydrazone tautomerism observed from UV-vis spectra by pH control and metal-ion complexation for two heterocyclic disperse yellow dyes

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Abstract

The azo-hydrazone tautomerism of two pyridine-2,6-dione based Disperse Yellow dyes has been achieved by pH control and metal-ion complexation, respectively, which is evidenced by UV-visible spectra using pH-titration, 1H NMR and X-ray single-crystal diffraction techniques for two dyes and one neutral dinuclear dye–metal complex. pH-titration experiments under strong and weak acidic conditions (HCl and HOAc) as well as strong and weak alkaline conditions (NaOH and ammonia) demonstrate that there is an equilibrium between the azo (HL1-A and HL2-A) and hydrazone (HL1-H and HL2-H) tautomers for two dyes in solution but the hydrazone form is dominant under conventional conditions. The hydrazone proton is also observed in the 1H NMR spectra of HL1-H and HL2-H which can be verified by the hydrogen–deuterium exchange and the presence of cooperative six-membered intramolecular hydrogen rings involving the hydrazone proton in their X-ray single-crystal structures. Moreover, the azo-hydrazone tautomerism is evidenced by the formation of a novel neutral dinuclear dye–metal complex Cu2(L2-A)4, where all the ligands are in the azo form and two types of coordination modes are present for four L2-A ligands. Namely, the side two ligands serve as the bidentate capping ligands, while the middle ones act as the quadridentate bridging ligands linking adjacent CuII centers in a reverse fashion.

Graphical abstract: Azo-hydrazone tautomerism observed from UV-vis spectra by pH control and metal-ion complexation for two heterocyclic disperse yellow dyes

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Publication details

The article was received on 22 May 2012, accepted on 06 Jul 2012 and first published on 09 Jul 2012


Article type: Paper
DOI: 10.1039/C2DT31102J
Citation: Dalton Trans., 2012,41, 11107-11115
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    Azo-hydrazone tautomerism observed from UV-vis spectra by pH control and metal-ion complexation for two heterocyclic disperse yellow dyes

    X. Chen, T. Tao, Y. Wang, Y. Peng, W. Huang and H. Qian, Dalton Trans., 2012, 41, 11107
    DOI: 10.1039/C2DT31102J

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